The present embodiments relate to magnetic resonance imaging (MRI) of a volume. The increase of the field strength and bore size of newer MRI imaging machines provides the opportunity for improved image resolution, quality, and patient comfort. A challenge with these systems is localized distortion in the volumes caused by the increase in magnetic field variation (B0) and gradient non-linearity. MRI volumes are susceptible to B0 and gradient non-linearity distortions as the distance from the magnet isocenter increases. The distortions reduce the reliable representation of scanned structure at the periphery of the acquired volumes.
Whole body MRI scans of a patient may be formed from 3-5 individual, high resolution volume acquisitions which are composed together to capture a complete scan of the patient. Since B0 and gradient distortion effects are most evident in the leading or trailing edges of a MRI volume, the intersections of neighboring volumes in a series tend to be unreliable, interfering with proper composing. Either (or both) of the edges of the neighboring volumes may be effected by distortion. Therefore, it is not readily deducible to determine how to correctly compose overlapping regions. Anatomy measurements in the overlapping regions may not be reliably trusted.
To avoid distortion, a continuous motion low-resolution scan (e.g., Siemens TIMCT whole-body single scan scout protocol) samples the patient only at the isocenter. The movement of the patient by the patient bed is relied on to place different positions of the patient at the isocenter in an ongoing scan. This scan is resistant to peripheral distortion. However, the number of MRI scanners with the ability to generate CT-like continuous scans is limited.
The distortion may be reduced or corrected in part by phantom calibration and feedback sensors. The distortion is detected and used to adjust the MRI scanner. However. B0 and gradient distortion are not completely solvable using calibration techniques either with or without a phantom since the mass/density distribution is idiosyncratic to a particular subject being scanned. The differences between patient and phantom and other transient effects degrade performance of calibration techniques.